Field
Example aspects described herein relate generally to optical communication networks, and, more particularly, to intranodal reconfigurable optical add/drop multiplexer (ROADM) fiber management apparatuses, and methods and systems employing the apparatuses.
Description of Related Art
Wavelength-division multiplexing (WDM) optical networks are presently dominated by 10 gigabit per second (Gb/s) transmission on dispersion-managed fiber plants. Such networks are typically comprised of multiple nodes interconnected by WDM paths. Optical signals (also referred to interchangeably herein as “traffic”, “wavelengths”, and/or “channels”) that are communicated across WDM networks typically originate at a first endpoint (a source system) that is local to one of the nodes (e.g., by way of a transmitter portion of local transponder) and terminate at a second endpoint (a destination system) that is local to another one of the nodes (e.g., by way of a receiver portion of local transponder). In some cases traffic is communicated from a source system at a source node to a destination system at a destination node without traversing any intermediate nodes. In other cases traffic is communicated from a source system at a source node to a destination system at a destination node by way of one or more intermediate nodes.
To facilitate the flow of traffic from source endpoints to destination endpoints throughout the network, each of the nodes includes a reconfigurable optical add/drop multiplexer (ROADM). As described in further detail below in the context of the various figures herein, a ROADM (which for convenience is also referred to interchangeably herein as a “node”) typically includes one or more bidirectional WDM ports coupled to other nodes of the network by way of one or more bidirectional WDM paths that carry WDMs signals each having multiple individual channels. Each of the bidirectional WDM ports of the ROADM is referred to herein as a degree and includes an ingress WDM port and a corresponding egress WDM port. The ROADM also includes one or more local add ports and/or local drop ports coupled to one or more local source systems and/or destination systems, respectively, from which traffic may originate and/or terminate.
The ROADM of a particular node facilitates the flow of traffic through that node of the network by receiving traffic either from a source system local to that node by way of a local add port, or from another node by way of an ingress WDM port, and, depending on the intended destination for the traffic, routing the traffic either to a destination system local to that node by way of a local drop port, or to another node by way of an egress WDM port. Traffic that a ROADM receives by way of its ingress WDM port from another node of the network and routes by way of its egress WDM port to another node of the network is referred to as “express traffic.”
Traffic that a ROADM either receives from a source system local to that node or routes to a destination system local to that node is referred to as “local traffic.” More particularly, traffic that a ROADM receives from a source system local to that node by way of a local add port, and routes by way of its egress WDM port to another node of the network is referred to as “local add traffic.” Traffic that a ROADM receives by way of an ingress WDM port from another node of the network, and routes by way of a local drop port to a destination system local to the node is referred to as “local drop traffic.”
Carriers are beginning to build all-coherent networks to fulfill rising 100 Gb/s service demands and expand network capacity. Although 100 Gb/s is the initial target data rate, some operators desire that new networks also support future 400 Gb/s data rates. In order to support faster data rates and/or provide additional functionality, modifications to ROADM/node architectures may be needed.
Each ROADM includes multiple components (e.g., a line subsystem, an add/drop subsystem, and local transponders), which are coupled to one another by way of intranodal optical fiber paths. Each of the ROADM components may be implemented according to one of several different architectures, and therefore any particular ROADM can be implemented according to one of numerous possible configurations. New node architectures should be flexible enough to support additional functionality and/or future transmission formats and as they become available. For instance, fixed filtering using a wavelength selective switch (WSSs) and a fixed add/drop structure (e.g., a fixed filtered AWG) may not fulfill the needs of 400 Gb/s service, which may require variability in bandwidth. In such a case, flexible grid wavelength selective switches (WSS) and add/drop elements with programmable center frequencies and bandwidths (i.e. colorless add/drop elements) may be desirable to provide colorless functionality. In some cases, in addition to colorless functionality, further architectural enhancements may be desired, such as colorless and directionless (CD) functionality employing a route-and-select WSS and a directionless add/drop element, and/or colorless, directionless, and contentionless (CDC) functionality employing a contentionless add/drop element as well.
Additionally, node modifications may also be needed to configure the node to accommodate an increased number of degrees and/or an increased number of add/drop modules, depending on the particular application. Thus, node configurations may vary from node to node and may change over time as needs evolve.
Management of the numerous intranodal optical fiber paths to be established between ROADM components (e.g., between the line subsystem and the add/drop subsystem) can be complex and burdensome, and the complexity and burden are only compounded by the needs for node architecture modification and flexibility described above. Installation and maintenance of the intranodal fiber paths can be operationally difficult and prone to error.
In some cases, fiber ribbon cables (each of which includes multiple, e.g., 12, fibers) may be employed to reduce the number of cables employed for establishing intranodal fiber paths. Such ribbon cables typically are terminated by a single multiple-fiber push-on/pull-off (MPO) connector at each end that contains all 12 terminating fibers. However, as shown in FIG. 4 (described in further detail below), a ROADM is often configured such that its intranodal fiber paths are meshed, in that fibers from a single module of the ROADM are routed to a variety of other modules of the ROADM. Therefore, although coupling MPO-to-MPO ribbon cables directly between ROADM modules may decrease the complexity of managing the intranodal fiber paths somewhat, such an approach may not enable the ROADM to provide the mesh topology often required of intranodal ROADM paths.